1. Field of the Invention
An apparatus consistent with the present invention relates to a linear compressor and, more particularly, to a linear compressor having a resonance spring of an improved structure.
2. Description of the Related Art
Generally, different from a reciprocating compressor, a linear compressor is of a free-piston structure having no connecting rod to restrict movement of a piston. The linear compressor comprises an outer casing to seal a predetermined space, a compressing part accommodated in the outer casing to suck and compress/discharge refrigerant gas and a driver to operate the compressing part by electric power from the outside.
The compressing part comprises a cylinder block forming the compressing chamber, a piston reciprocatably provided in the compressing chamber and a cylinder head having a sucking valve to suck a refrigerant gas in the compressing chamber and a discharging valve to discharge the refrigerant gas.
The driver comprises an inner core provided outside of the cylinder block, an outer core spaced apart from a circumferential surface of the inner core, a magnet provided between the outer core and the inner core to reciprocate in a perpendicular direction by interacting with a magnetic field generated between the inner and outer cores due to electric power from the outside. A reciprocating member having a first part connected with an upper part of the piston and a second part connected to the magnet of the driver is provided on the compressing part to reciprocate with the piston and the magnet as a single body. A resonance spring connected with reciprocating member and the outer core of the driver is provided on the reciprocating member to facilitate a reciprocation of the piston.
Generally, the reciprocation of the piston depends on a stiffness due to the gas pressure in the compressing chamber, a stiffness of the resonance spring, the weight of the piston and a driving force of the driver.
The stiffness of the gas pressure in the compressing chamber is reduced when the discharging valve is opened. That is, if the stiffness of the gas pressure in the compressing chamber is increased when the refrigeration gas is compressed and reduced when the refrigeration gas is discharged. An average stiffness with respect to the average gas pressure in the compressing chamber has a highly nonlinear property as the maximum displacement of the piston is varied.
The stiffness of the resonance spring may be represented as an elastic force of the resonance spring per a unit displacement.
If the weight of the piston and the driving force of the driver are constant, the reciprocating motion of the piston mainly depends on the stiffness of the resonance spring and the stiffness or resistance of the gas pressure in the compressing chamber. The stiffness of the resonance spring and the resistance of the gas pressure in the compressing chamber facilitate the efficient operation of the linear compressor. For greater efficiency, it is better if a natural frequency according to the addition of the stiffness of the resonance spring and the average stiffness with respect to the gas pressure remains approximately the same as a frequency of the electric power.
As shown in FIG. 1, the conventional resonance spring 150 is of a disk shape and comprises a first connecting part 151 connected with the outer core (not shown) at a circumferential part and a second connecting part 155 connected with the reciprocating member (not shown) in the center to reciprocate with the reciprocating member as a single body. The resonance spring 150 is formed with a plurality of through holes 159 of a spiral shape between the first connecting part 151 and the second connecting part 155, which forms a plurality of arms 160.
The first connecting part 151 is formed with a plurality of first connecting holes 153 so as to be fixedly connected with the outer core by bolts passing therethrough and the second connecting part 155 is provided with a second connecting hole 157 to permit connection with the reciprocating member by a bolt passing therethrough.
Thus, the first connecting part 151 of the conventional resonance spring 150 is fixed with the outer core of the driver and the second connecting part 155 thereof is reciprocatably connected with the reciprocating member, which facilitates the reciprocation of the piston.
However, the first connecting holes 153 of the conventional linear compressor are formed also at a part at which the first connecting part 151 and the arm 160 are connected. Thus, the first connecting part 151 is not deformed with respect to the outer core of the driver, when the reciprocating member reciprocates. In the conventional linear compressor, only the second connecting part 155 is twisted—deformed with respect to the first connecting part 151. Accordingly, the stiffness of the conventional resonance spring 150 has an approximately linear property, so that the stiffness is approximate linearly changed as the maximum displacement is changed.
As shown in FIG. 2, the average stiffness or resistance b of the gas pressure constantly decreases in a narrow-range for maximum displacement at a small displacement section X1, and radically decreases highly nonlinearly for maximum displacement at a large displacement section X2. The stiffness a of the conventional spring remains constant and has an approximately linear property in both the small displacement section X1 and the large displacement section X2.
Thus, an addition c of the stiffness a of the conventional spring and the average stiffness b of the gas pressure remains fairly constant in the small displacement section X1 but still radically decreases in the large displacement section X2.
Accordingly, the conventional linear compressor can be used only in the small displacement section X1 in which the addition c of the stiffness a of the conventional spring and the average stiffness b of the gas pressure remains fairly constant and approximately the same as the frequency of the electric power, thereby causing a problem in that the conventional linear compressor cannot be used in the large displacement section X2 in which the average stiffness of the gas pressure is radically changed with a highly nonlinear property.